Semiconductor processing builds hundreds of individual IC (also called semiconductor) chips on a wafer. These individual chips are then tested, assembled, and packaged for their various uses. The packaging step can be an important step in terms of costs and reliability. The individual IC chip must be connected properly to leads (leading to external circuitry) and packaged in a way that is convenient for use in a larger circuit or electrical system.
Prior to packaging, the wafers containing the numerous IC chips are thinned from the side of the wafer away from the chips. The wafers are then mounted to an adhesive tape and cut into individual chips, typically using a dicing saw. The chips are then mounted onto a metal lead frame or on a metallized region of an insulating substrate. In this process, a thin layer of a metal (such as Au, optionally combined with Ge or other elements to improve the metal contact) is placed between the bottom of the chip and the metal lead frame/insulated substrate. Heat (and optionally a slight pressure) can then be applied to form an alloyed bond holding the chip firmly to the substrate.
Once the chips are mounted by this process, the chips are then wire bonded to the lead frame. This wire bonding is typically performed by attaching interconnecting wires from various contact pads on the IC chip to corresponding posts on the lead frame. The time used to bond wires individually to each pad on the chip can be overcome by several methods that utilize simultaneous bonding, i.e., the flip-chip approach. In this approach, relatively thick metal bumps are deposited on the contact pad before the chips are separated from the wafer. A matching metallization pattern is also provided on the substrate. After separation from the wafer, each chip is turned upside down and the bumps are properly aligned with the metallization pattern on the substrate. Then, ultrasonic bonding or solder alloying aids the attachment of each bump to its corresponding metallization pattern on the substrate.
The resulting device is then packaged in any suitable medium that can protect it from the environment of its intended use. In most cases, this means that the device is isolated from moisture, contaminants, and corrosion. The packaging used for such protection can be either hermetic-ceramic or plastic. In a plastic package, the chip is encapsulated with resin materials, typically epoxy-based resins.
FIGS. 4 and 5 depict an IC chip with a typical plastic package having a source 201, gate 202, and drain 203. The chip/die 206 is attached to the central support 207 of the lead frame. The frame, made of etched or stamped thin metal (e.g., Fe—Ni or Cu alloys), includes external leads 205 and the interconnections provided by the bond wires 204 are typically fine gold wires. The encapsulation 208 is often accomplished by a molding process that uses an epoxy resin to cover the chip and form the outer shape of the package at the same time. The external portions of the lead frame can be shaped as a gull wing lead or a j-lead (as depicted in FIG. 5).
Such prior art devices however, suffer from several problems. Namely, such devices have a relatively high drain-source resistance (RDS(on)), a large footprint, a high profile, a poor package inductance, an inefficient thermal performance, and often require complex manufacturing processes.